1. Field of the Invention
This invention relates to decoders for generating audio signals from digital data, and in particular to combined audio and video decoding according to the MPEG standard.
2. Description of Related Art
The Motion Picture Experts Group (MPEG) developed an international standard (sometimes referred to herein as the "MPEG standard") for representation, compression, and decompression of motion pictures and associated audio on digital media. The International Standards Organization (ISO) publication, No. ISO/IEC 11172: 1993 (E), entitled "Coding for Moving Pictures and Associated Audio - for digital storage media at up to about 1.5 Mbit/s," describes the MPEG standard and is incorporated by reference herein in its entirety. The MPEG standard specifies coded digital representations of audio and video and is intended for continuous data transfer from equipment such as compact disks, digital audio tapes, or magnetic hard disks, at rates up to 1.5 Mbits per second.
Under the MPEG standard, parallel data streams or time multiplexed data streams provide video data frames and audio data frames. Methods and systems for decompressing video data frames are described in U.S. patent applications Ser. Nos. 07/890,732, now abandoned, and 07/669,818, now abandoned, which were incorporated by reference above. Audio data frames contain a header, side information, and subband data. Subband data indicate frequency-domain vectors that are converted to time-domain output sound amplitudes by a transformation (matrixing) and a smoothing filter (windowing).
Typically, MPEG audio/video decoding systems for decoding digital data include, two decoders, one for audio decoding and one for video decoding, on two separate integrated circuit chips. The audio decoder and video decoder are separated because of the differences between MPEG audio coding techniques and MPEG video coding techniques, but separate audio and video decoders increase the amount of circuitry in and the cost of an audio/video decoding system. A decoding architecture is needed that reduces the amount of circuitry and the cost of decoding MPEG audio and video data.